1. Field of the Invention
The present invention relates to so-called projector type vehicle headlamp.
2. Description of the Related Art
In general, a projector type vehicle headlamp has such a structure that a projection lens is provided on an optical axis extended in the longitudinal direction of the vehicle, and furthermore, a light source is provided on a rear side from a focal point on a back side thereof and a light emitted from the light source is reflected toward the optical axis by means of a reflector.
As disclosed in JP(UM) Hei 2-47704 and JP(A) 2001-229715, there described the structure of a so-called side insertion type lighting unit in which a light source is constituted by the light emitting portion of a light source bulb inserted and fixed into a reflector from the side of an optical axis in the projector type vehicle headlamp.
Moreover, JP (A) Hei 4-39137 or JP (A) Hei 10-223002 describes the structure of a lighting unit in which an annular light transmitting member is provided along the outer peripheral edge portion of a projector lens between the projector lens and a reflector in the projector type vehicle headlamp.
By employing the structure of the side insertion type lighting unit described in the JP(UM) Hei 2-47704 and the JP(A) 2001-229715, it is possible to decrease the longitudinal length of the lighting unit, thereby causing the lighting unit to be compact. Since the light source bulb is inserted and fixed into the reflector over the same horizontal plane, there are the following problems.
More specifically, in the projector type vehicle headlamp, an optical-axis side region in the reflecting plane of the reflector is suitable for forming the diffusing region of a light distribution pattern. In this case, however, the light source bulb is inserted and fixed into the reflector over the same horizontal plane as the optical axis, resulting in a hole for inserting and fixing the light source bulb being formed on the optical-axis side region of the reflecting plane. For this reason, the optical-axis side region cannot be utilized effectively for a light distribution control. Therefore, there is a problem in that it is hard to maintain sufficient amount of the brightness of the diffusing region of the light distribution pattern.
On the other hand, in the structure of the side insertion type lighting unit, if the annular light transmitting member described in JP-A-4-39137 or JP-A-10-223002 is provided, a direct light emitted from the light source toward the outer peripheral space of the projection lens can be irradiated on the forward part of the lighting unit. Consequently, it is possible to effectively utilize the luminous flux of the light source and to increase the amount of a light to be irradiated on the forward part of the vehicle.
In the structure of the side insertion type lighting unit, however, there is a problem in that the irradiated light cannot be controlled by the annular light transmitting member with high precision if the annular light transmitting member is simply provided.